Why non-explicit splat param plus default param is wrong syntax for method definition in Ruby 1.9?

Question

I'd like to ask why having a splat param1 and a param2 with default value assignment in Ruby-1.9.3-p0 as below:

def my_method(*param1, param2 = "default"); end

returns

SyntaxError: (irb):1: syntax error, unexpected '=', expecting ')'

My workaround is explicitly wrap param1 in brackets like this:

def my_method((*param1), param2 = "default"); end

Many thanks

Marc is right, your work around doesn't actually work. Try `o.my_method(1, 2, 3)` and see what happens. — mu is too short, Feb 06 '12 at 02:01

score 7 · Accepted Answer · edited Feb 06 '12 at 05:15

Ruby can't parse a parameter with a default after a splat. If you have default assignment in a parameter after a splat, how would Ruby know what to assign the variable to?

def my_method(*a, b = "foo"); end

Let's say I then call my_method:

my_method(1, 2, 3)

Ruby has no way of knowing whether b is missing, in which case you want b to be foo and a is [1,2,3], or if b is present in which case you want it to be 3.

Why non-explicit splat param plus default param is wrong syntax for method definition in Ruby 1.9?

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